Unlike the performance inspection (which is often done during a real estate transaction when emotions are high & resources such as time and patience are limited), a maintenance assessment is typically done for a homeowner who has a genuine concern with how their system is functioning and is curious if there is anything that can be done to help it keep working for as long as possible.
A proactive seller might do a maintenance assessment when preparing for their sale. It's prudent to find out how the system is functioning and to take care of any remediation that might be needed ahead of time.
The maintenance assessment entails much of the same tasks done during a performance and a compliance inspection.
Regardless of the type of system & regulations of its day, the goal of the inspection is generally the same: to locate & assess how the system is performing based on the intention of its design.
If needed, the maintenance assessment includes maintenance and remediation techniques to bring the system back on line and functioning how it was intended.
If/when the system is operating substantially as intended a Maintenance Plan is created for the system tailored to its unique needs.